Absence of detectable 5-methylcytosine in DNA of embryos of the brine shrimp, Artemia

Ageing European lobsters (Homarus gammarus) using DNA methylation of evolutionarily conserved ribosomal DNA

Crustaceans are notoriously difficult to age because of their indeterminate growth and the moulting of their exoskeleton throughout life. The poor knowledge of population age structure in crustaceans therefore hampers accurate assessment of population dynamics and consequently sustainable fisheries management. Quantification of DNA methylation of the evolutionarily conserved ribosomal DNA (rDNA) may allow for age prediction across diverse species. However, the rDNA epigenetic clock remains to be tested in crustaceans, despite its potential to inform both ecological and evolutionary understanding, as well as conservation and management practices. Here, patterns of rDNA methylation with age were measured across 5154 bp of rDNA corresponding to 355 quality-filtered loci in the economically important European lobster (Homarus gammarus). Across 0- to 51-month-old lobsters (n = 155), there was a significant linear relationship between age and percentage rDNA methylation in claw tissue at 60% of quality-filtered loci (n = 214). An Elastic Net regression model using 46 loci allowed for the accurate and precise age estimation of individuals (R 2 = 0.98; standard deviation = 1.6 months). Applying this ageing model to antennal DNA from wild lobsters of unknown age (n = 38) resulted in predicted ages that are concordant with estimates of minimum size at age in the wild (mean estimated age = 40.1 months; range 32.8-55.7 months). Overall, the rDNA epigenetic clock shows potential as a novel, nonlethal ageing technique for European lobsters. However, further validation is required across a wider range of known-age individuals and tissue types before the model can be used in fisheries management.

Quantitative DNA-methylation in Daphnia magna and effects of multigeneration Zn exposure

Little research on the epigenetic phenomenon of DNA methylation has been performed with invertebrates. However, a few studies have shown that effects of transient chemical exposure can be transferred to non-exposed generations through epigenetic inheritance. If this is a wide-spread phenomenon it may have major consequences for current ecological risk assessments. The presence of DNA methylation in Daphnia magna has only very recently been demonstrated, although not quantified. In the present study, the overall content of 5-methyl-2'-deoxycytidine (5 mdC) in the DNA of D. magna was determined. Additionally, the effect of transgenerational Zn exposure on the 5 mdC content was assessed. An optimized LC-MS-MS method proved to be very suitable for measuring overall levels of 5 mdC in relatively small samples of D. magna DNA. The average [5 mdC]/[dG] ratio ranged from 0.13% to 0.81%. A slight but significant decrease in DNA methylation was found in the offspring (F1) of Zn exposed daphnids in the parental generation. However, this effect did not propagate into the next generation (F2). The presence of DNA methylation in D. magna and the finding that different exposure histories can entail different levels of methylation, open the way for further investigations on the implications of epigenetics in aquatic toxicology.

Characterization of a group 1 late embryogenesis abundant protein in encysted embryos of the brine shrimp Artemia franciscana

Late embryogenesis abundant (LEA) proteins are hydrophilic molecules that are believed to function in desiccation and low-temperature tolerance in some plants and plant propagules, certain prokaryotes, and several animal species. The brine shrimp Artemia franciscana can produce encysted embryos (cysts) that enter diapause and are resistant to severe desiccation. This ability is based on biochemical adaptations, one of which appears to be the accumulation of the LEA protein that is the focus of this study. The studies described herein characterize a 21 kDa protein in encysted Artemia embryos as a group 1 LEA protein. The amino acid sequence of this protein and its gene have been determined and entered into the NCBI database (no. EF656614). The LEA protein consists of 182 amino acids and it is extremely hydrophilic, with glycine (23%), glutamine (17%), and glutamic acid (12.6%) being the most abundant amino acids. This protein also consists of 8 tandem repeats of a 20 amino acid sequence, which is characteristic of group 1 LEA proteins from non-animal species. The LEA protein and its gene are expressed only in encysted embryos and not in larvae or adults. Evidence is presented to show that the LEA protein functions in the prevention of drying-induced protein aggregation, which supports its functional role in desiccation tolerance. This report describes, for the first time, the purification and characterization of a group 1 LEA protein from an animal species.

Identification of a novel DNA methyltransferase 2 from the brine shrimp, Artemia franciscana

DNA methyltransferase 2 (Dnmt2) is a dual-specificity DNA methyltransferase, which contains a weak DNA methyltransferase and novel tRNA methyltransferase activity. However, its biological function is still enigmatic. To elucidate the expression profiles of Dnmt2 in Artemia franciscana, we isolated the gene encoding a Dnmt2 from A. franciscana and named it as AfDnmt2. The cDNA of AfDnmt2 contained a 1140-bp open reading frame that encoded a putative Dnmt2 protein of 379 amino acids exhibiting 32% approximately 39% identities with other known Dnmt2 homologs. This is the first report of a DNA methyltransferase gene in Crustacean. By using semi-quantitative RT-PCR, AfDnmt2 was found to be expressed through all developmental stages and its expression increased during resumption of diapause cysts development. Southern blot analysis indicated the presence of multiple copies of AfDnmt2 genes in A. franciscana.

DNA methylation, histone H3 methylation, and histone H4 acetylation in the genome of a crustacean

In this work, we used antibodies against histone H3 trimethylated at lysine 9 (H3K9m3); against histone H4 acetylated at lysines 5, 8, 12, and 16 (H4ac); and against DNA methylated at 5C cytosine (m5C) to study the presence and distribution of these markers in the genome of the isopod crustacean Asellus aquaticus. The use of these 3 antibodies to immunolabel spermatogonial metaphases yields reproducible patterns on the chromosomes of this crustacean. The X and Y chromosomes present an identical banding pattern with each of the antibodies. The heterochromatic telo meric regions and the centromeric regions are rich in H3K9m3, but depleted in m5C and H4ac. Thus, m5C does not seem to be required to stabilize the silence of these regions in this organism.Key words: DNA methylation, H3 methylation, H4 acetylation, crustacean, Asellus aquaticus.

Caenorhabditis elegans DNA does not contain 5-methylcytosine at any time during development or aging

DNA, isolated from age-synchronous senescent populations of Caenorhabditis elegans has been quantitatively and qualitatively analyzed for the presence of 5-methylcytosine. High performance liquid chromatography on two wild-type and several mutant strains of C. elegans failed to detect any 5-methylcytosine. The restriction endonuclease isoschizomers, HpaII and MspI, were used to digest genomic DNA after CsCl purification and failed to detect any 5' cytosine methylation at any age. We conclude that C. elegans does not contain detectable (0.01 mole percent) levels of 5-methylcytosine.